Method and device for bonding of chips

ABSTRACT

A method and device for bonding chips onto a substrate or onto further chips. The chips are bonded onto the substrate or the further chips by means of a direct bond.

RELATED APPLICATIONS

The present application is a divisional of U.S. application Ser. No.16/483,077, filed Aug. 2, 2019, which is a U.S. National StageApplication of International Application No. PCT/EP2017/054971, filedMar. 2, 2017, said patent applications hereby fully incorporated hereinby reference.

FIELD OF THE INVENTION

The invention relates to a method and a device for bonding chips.

BACKGROUND OF THE INVENTION

Chip-to-wafer (C2 W) or chip-to-chip (C2C) processes are described inthe prior art via solder balls or copper pillars with solder caps.However, the solder balls or copper pillars with solder caps,respectively, are extremely large and increase the thickness of thechips produced in this way.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved bondingmethod or an improved bonding device, respectively, or an improvedproduct, respectively.

This object is solved by means of the subject matter of the independentpatent claims. Advantageous further developments of the invention arespecified in the subclaims. All combinations of at least two featuresspecified in the description, the claims and/or the figures also fallwithin the scope of the invention. In the case of specified valueranges, values within the mentioned boundaries shall also be consideredas being disclosed as threshold values and shall be capable of beingclaimed in any combination.

According to the invention, provision is made for a method for bondingchips onto a substrate, in particular semiconductor substrate, or ontofurther chips, wherein the chips are bonded onto the substrate or thefurther chips by means of a direct bond. A direct bond is understood tobe a bond, which forms directly via the interaction of two surfaces,without forming a liquid phase. According to another term definition, adirect bond is understood to be a bond, in the case of which noadditional materials need to be used. A direct bond is in particularunderstood to be a metal-metal solid body bond, in particular diffusionbond, a prebond or a fusion bond resulting from the prebond,respectively, or a hybrid bond, i.e. a bond, which is based on fusionbond portions and metal bond portions.

According to the invention, provision is furthermore made for a devicefor bonding chips onto a substrate or further chips, wherein the chipscan be bonded onto the substrate or the further chips by means of adirect bond.

According to the invention, provision is furthermore made for a chipstack of chips, wherein the chips are bonded to one another by means ofa direct bond.

According to the invention, provision is furthermore made for asubstrate comprising chips (product), wherein the chips are bonded ontothe substrate by means of a direct bond.

According to the invention, a direct bond option on C2C or C2 W level ismade possible. Advantageously, solder balls or copper pillars withsolder caps are no longer required. The thicknesses of the produced chipstacks or products, respectively, become smaller, the throughput isincreased and the efficiency of the chip communication increases. Thedirect bond in particular has a bond strength of more than 0.1 J/m²,preferably more than 0.5 J/m², more preferably more than 1.0 J/m², mostpreferably more than 2.0 J/m², most preferably of all more than 2.5J/m². The direct bond in particular occurs at temperatures of less than400° C., preferably less than 300° C., more preferably at less than2000° C., most preferably less than 150° C., most preferably of all lessthan 100° C. The direct bond furthermore occurs without the productionof a liquid phase.

The invention is based on the idea of keeping the surface of a chip soclean that a following direct bond step can occur. The chips prepared inthis way comprising a contamination-free bond surface can then be bondedonto the substrate (chip-to-wafer, C2 W) or onto other chips(chip-to-chip, C2C).

In the further course of the present disclosure, a substrate orsemiconductor substrate, respectively, is understood to be a not yetseparated, in particular round, semi-finished product or thesemiconductor industry. Particularly preferably, a substrate is a wafer.The substrates can have any shape, but are preferably circular. Thediameter of the substrates is in particular standardized in theindustry. For wafers, the industry-standard diameters are 1 inch, 2inches, 3 inches, 4 inches, 5 inches, 6 inches, 8 inches, 12 inches and18 inches. On principle, however, the embodiment according to theinvention can handle every substrate, regardless of the diameterthereof.

In the further course of the present disclosure, a chip will beunderstood to be a mostly rectangular part, which is obtained byseparation of a semiconductor substrate (wafer). A chip typicallyincludes an integrated circuit, which is created in response to treatingthe semiconductor substrate.

In the present disclosure, a bond surface is understood to be a surface,which will become part of a bond boundary surface at some point during aprocess. Specifically, the bond surface is understood to be the surfaceof a chip, which needs to be treated according to the invention, inparticular cleaned, before the chip is bonded. If a chip is bonded ontoa substrate, the substrate surface can also be identified as bondsurface.

In a preferred embodiment, the bond surfaces are hybrid bond surfaces. Ahybrid bond surface is understood to be a bond surface, which iscomprised of metallic and dielectric regions and thus of metallic anddielectric bond surface parts. All of the methods and/or devicesmentioned in the present disclosure, which refer to the direct bond ingeneral, can thus be used for the bonding of hybrid surfaces.Preferably, the metallic and dielectric surface parts are largelylocated in one plane. In particular, the metallic surface parts arerecessed with respect to the dielectric surface parts or protrude withregard to the dielectric surface parts by the less than 0.5 μm,preferably less than 100 nm, more preferably less than 50 nm, mostpreferably less than 10 nm.

Cleaning Method

In the further course of the present disclosure, a cleaning isunderstood to be the removal of contaminations of the bond surface bymeans of one and/or a plurality of the following methods:

wet-chemical cleaning, in particular

-   -   with water, in particular        -   CO2-containing water    -   with alcohols    -   with acids, in particular        -   formic acid        -   citric acid        -   peroxomonosulphuric acid        -   standard clean 1 (SC1)        -   standard clean 2 (SC2)    -   with bases, in particular        -   NH4OH

plasma cleaning

plasma incineration

mechanical cleaning, in particular

-   -   brushing

A plasma cleaning is understood to be the generally highly energeticbombardment of a surface with the ionized parts of a plasma. The ions ofthe plasma are thereby accelerated by means of electrical and/ormagnetic fields and have a non-negligible penetration depth. A plasmacleaning can be associated with the plasma activation of a surface.

A plasma incineration is understood to be the generally low-energeticcleaning process of organic substances from a surface. The cleaningthereby occurs in particular by means of oxidation of the organicspecies, in particular with oxygen and/or fluorine or any other suitableand ionizable oxidizing agent. The organic components oxidized by meansof the plasma incineration are preferably discharged from the reactionchamber. This either occurs by means of a continuous flow of the plasmaor by means of a sequential aerating and deaerating of the plasmachamber. In a more preferred embodiment, the incinerated and oxidizedorganic components, however, are bonded within the plasma chamber bymeans of chemical and/or physical processes, so that their return to thesubstrate surface is prevented. Complicated devices, which require acirculation of the plasma, are thus avoided.

A wet-chemical cleaning by means of one or a plurality of theabove-mentioned liquids is optionally performed after the plasmaincineration, so as to thus even further improve the cleanliness of thesurface and/or the surface chemistry of the surfaces to be cleaned, inparticular by means of termination of the surfaces with suitable speciesfor the bonding, which are already known to the person of skill in theart. Advantageously, the method serves the purpose of removingparticles, which were created in particular in response to the plasmaincineration and/or which remained on the surface.

The cleaning of a bond surface can thus also be performed by means of aplurality of the mentioned methods. The cleaning can be performed on achip or simultaneously on a plurality of chips. In particular individualchips can be cleaned in response to the transport between two stations.

Self Alignment

In a preferred embodiment, the chips are positioned, and a selfalignment of the chips occurs. Self alignment is understood to be apositioning process of an object, in the case at hand of a chip, whichis driven by physical laws of minimization.

The self alignment preferably occurs in that the chip is driven on abond surface with extremely small adhesion, in particular caused by aliquid separated on the bond surface, into an, in particular centricalposition between features of the bond surface.

It would be conceivable for example that for example four metallicregions, in particular metallic bond surfaces, such as contact pads, arelocated on the bond surface, in particular as part of a hybrid bondsurface or vias. On its bond surface, the chip also has four regions. Ifone such chip is placed onto a liquid, it is to be assumed that morehydrophilic regions will position themselves above more hydrophilicregions and that more hydrophobic regions will position themselves abovemore hydrophobic regions. An alignment, in the case of which themetallic regions of the hybrid bond surfaces are made to be congruent,will thus occur.

It is clear to the person of skill in the art that such a self alignmentcan occur even better, the higher the symmetry of the structures, whichare involved in the self alignment. This includes the geometry of thechips, the distances between the metallic regions of the hybrid bondsurfaces, the shape of the metallic regions, etc. The chip shouldpreferably be square. The metallic regions of the hybrid bond surfaceshould furthermore preferably also be located at the corners of animaginary square. A further advantage would be at hand, if thedifference between the hydrophilicity and hydrophobicity of thecorresponding hybrid bond regions is as large as possible. The contactangle, which forms between a test liquid drop, in particular water, andthe surface to be measured, is one measure for the hydrophobicity orhydrophilicity, respectively. Hydrophilic surfaces flatten the liquiddrop, because the adhesion forces between the liquid and the surfacedominate over the cohesive forces of the liquid and thus form smallcontact angles. Hydrophobic surfaces lead to a spherical shape of theliquid drop, because the cohesive forces of the liquid dominate over theadhesive forces between the liquid and the surface. The contact angledifference between the two different mentioned hybrid bond regions ispreferably larger than 1°, preferably larger than 5°, more preferablylarger than 25°, most preferably larger than 50°, most preferably of alllarger than 100°.

The liquid layer applied to the bond surface has a thickness of lessthan 2 mm, preferably less than 1.5 mm, more preferably less than 1 mm,most preferably less than 0.5 mm, most preferably of all less than 0.1mm. The liquid is preferably water. However, the use of any otherliquid, such as

alcohols

ethers

acids

bases

is conceivable as well. In particular ethers have a very high steampressure and thus evaporate almost completely from the surface, whichautomatically leads to a removal of the liquid after the attained selfalignment. Advantageously, a pre-bond is automatically created betweenthe surfaces after the removal of the liquid.

In a particular embodiment according to the invention, grooves, whichfacilitate or first provide for the removal of the liquid after the selfalignment of the chip, are located on the bond surface of the substrateand/or of the chip, in particular in the dielectric regions. Thesegrooves preferably lead from the region of the chip surface to the edgeof the chip, so that the liquid can be removed to the outside by meansof flowing and or evaporating, preferably automatically, more preferablywith the support of the force of gravity, which leads to the liquidbeing pressed out.

Bonding Devices and Methods

A plurality of devices and processes according to the invention forbonding chips are disclosed. The methods according to the invention canbe divided into individual bonding methods and collective bondingmethods. The corresponding devices are thus devices for the individualbonding or for the collective bonding, respectively. All methods anddevices according to the invention have in common that the bond surfacesof the chips need to be contamination-free until the bonding process.The process steps and systems according to the invention for reachingthis goal will be described in more detail below.

Individual Bonding Devices and Methods

An individual bonding method is understood to be the processes, whichare common in the prior art, for placing chips individually, i.e.consecutively, onto other chips (C2C) or onto a wafer (C2 W). Suchmethods have the advantage that chips of different sizes and/or ofdifferent functionality can be bonded.

Separation on a Tape

In a first exemplary method according to the invention, a substrate isfixed onto a carrier, in particular a tape, and is separated into chipsthere. In the further course of the present disclosure, the tape will beused as an exemplary example. However, the use of a rigid carrier isconceivable as well. The chips are thus only produced, after thesubstrate has been fixed onto the tape.

In a first process step of the method, the fixation of the carrier, inparticular of the tape, occurs on a fixation, in particular a dicingframe. If the carrier is a rigid carrier, this process step can beforgone, or the rigid carrier can be fixed to a substrate holder/carrierholder, respectively.

In a second, optional process step, the bond surface of the substrate,from which the later bond surfaces of the chips are produced, iscleaned. The cleaning can be one of the already-mentioned cleaningtypes. In particular, the cleaning occurs by means of plasma and/orliquids and/or gases. In addition, a plasma treatment preferably leadsto a plasma activation of the bond surface. The bond surface then onlyneeds to be cleaned, if it has been contaminated by preceding processesin such a way that the contaminations are also transferred to the tape,or that contaminations are present, which would later prevent and/ornegatively impact the formation of a direct bond. However, a cleaning ofthe bond surface of the substrate always occurs prior to the fixation.

In a third process step according to the invention, the substrate isfixed to the carrier with its, in particular cleaned, preferablyplasma-activated bond surface. According to the invention, the tape isthereby designed in such a way that the contamination of the bondsurface is as small as possible after the substrate is removed from thecarrier. If the carrier is a rigid carrier, it may be necessary toprovide the carrier surface with a protective layer prior to thefixation of the substrate. In the case of tapes, such a protective layeris already present for the most part.

Starting at the time of the contacting of the bond surface, the carrierfurthermore also serves as the protection thereof and prevents acontamination of the bond surface. At least in the center of thesubstrate, the carrier is preferably mostly coated in such a way that alow adhesion between the bond surface of the substrate and the carrierprevails, while the carrier can in fact have an adhesive property in theperipheral region of the substrate. The regions with a high adhesivestrength, thus with a higher adhesive force, will likely create acontamination on the substrate periphery, which can preferably beneglected, as long as no regions of the bond surface are affected, fromwhich chips will be produced later. The tape is preferably designed insuch a way that the adhesive force decreases by means of energy inputinto the tape (UV, heat) and the chips can thus be removed more easilylater. Such tapes are known in the prior art.

However, tapes with a particularly small contamination are preferablyused for the process according to the invention.

The tapes preferably have adhesives, which cannot penetrate into thebond surface, in particular into the reservoirs, which were produced bymeans of the plasma activation, which had been performed beforehand.This is preferably ensured in that the adhesives have a very highviscosity, which prevents a penetration into the nano-porous surface.More preferably, the molecules of the adhesive are so large that apenetration into the pores is not possible due to the large molecules.The pores are in particular smaller than 10 nm, more preferably smallerthan 5 nm, most preferably smaller than 1 nm, even more preferablysmaller than 0.5 nm, most preferably of all smaller than 0.2 nm. Thepore sizes are also disclosed in WO2012100786A1. It is most preferablethat the adhesives are solids, which are bonded in a polymer matrix.Preferably, a cleaning with solvents can be forgone by means of such adesign of the adhesives after removal of the tape, and a storage ofsolvents in the reservoir, which has been created by means ofplasma-activation on the surface of the bond surfaces, are thusprevented. This results in improved bonding results, because anoutgassing of the solvents after the bonding and thus the formation ofbubbles in the bond boundary surface can thus be prevented.

The production of such a reservoir is disclosed in publicationsWO2012100786A1, WO2012136267A1, WO2012136268A1, WO2012136266A1 andWO2014015899A1.

In a highly preferred embodiment according to the invention, however,the carrier is coated in such a way that it can fix the substrate acrossits entire surface, does not leave a contamination on the substrate andthe chips, which are produced later, can be removed easily.

In a fourth process step according to the invention, the substrate isseparated. The separation can be performed by means of any method, if itdoes not contaminate the bond surface. In the further course of thepresent disclosure, some separating methods will be discussed in moredetail, with the help of which it is ensured that the bond surface iskept clean according to the invention during the separation.

In a fifth process step according to the invention, the separated chipsare removed from the carrier by means of a machine, in particular a chipbonder. In a particularly preferred embodiment according to theinvention, a further, in particular continuous cleaning of the bondsurface of the chip occurs during the removal and/or during thetransport of the chip to a further position, in particular the bondposition. This cleaning preferably occurs by means of plasma. The chipsthereby either pass through a region, in which this cleaning occurs, orthe removal of the chips from the carrier occurs in a room, in whichthis cleaning property occurs automatically. It is thus conceivable, forexample, that the chips are removed from the carrier in a plasma chamberof the chip bonder. More preferably, the chips are moved past anatmospheric plasma source after the removal from the carrier. Inparticular, oxygen plasma is used, which preferably leads to theincineration of residues.

In a sixth process step according to the invention, the bond surface ofthe transported, separated chip is bonded with a second bond surface bymeans of a bond, in particular a direct bond or hybrid bond,respectively. An alignment process of the chip, which is generallyperformed relatively quickly, in relation to the second bond surface, towhich it is to be bonded, thereby precedes the bonding process.Improvements according to the invention for the optimal bonding will bementioned in more detail in other sections of the present disclosure.This alignment process preferably takes less than 5 seconds, morepreferably less than 2 seconds, most preferably less than 1 second.

Method for the Separation

An essential aspect of the embodiment according to the invention lies inkeeping the bond surface of a substrate or of the chips separatedtherefrom, respectively, clean. To ensure the cleanliness of the bondsurface, the separating processes also need to cause a smallest possiblecontamination. In particular, no burrs may be created in response to theseparation of a substrate. According to the invention, this can beensured by means of a plurality of different processes.

In a first possible process, the so-called stealth dicing, a focusedlaser beam changes the material properties in such a way that an easyseparation of the chips can occur. The advantage lies in particular inthat mechanical separating agents, such as cutting wheels, can beforgone. The general mode of operation of the stealth dicing process isknown in the prior art.

In a second possible process, the chips are separated from one anotherby the use of plasma.

In a third possible process, the chips are separated from one another bythe use of mechanical separating agents. In a highly preferredembodiment according to the invention, grooves are created on the bondside here prior to an optional cleaning of the bond surface and thefixation of the substrate onto the carrier. In response to theseparating process from the rear side of the substrate, the mechanicalseparating agents then hit the prefabricated grooves. By prematurelyreaching the mechanical separating agents in the empty space, thegrooves thus prevent a contamination of the bond surface of theindividual chips.

The grooves can preferably also be used in the above-mentionedseparating methods, because they can also lead to contaminations on theedge and/or burrs. In particular, when the breakage does not runcontinuously vertically through the wafer, in particular during thestealth dicing, for example due to the layer construction of the chips.The grooves are created in particular to avoid at least the formation ofa burr on the bond surface.

The grooves can also be the result of a masking process, which is usedin response to a deposition of a material on a surface. In response tosuch a process, no material is deposited at the masked locations. Themasked regions then form the grooves.

Collective Bonding Devices and Methods

It may be disadvantageous in certain circumstance to bond chips by meansof an individual bonding method. In particular when the bond surfaces ofthe chips need to be cleaned in order to obtain a high bond quality, itmay be advantageous, to first position all chips on a carrier in such away that the later bond surface points upwards. In this pre-fixation,all bond surfaces of the chips can then be cleaned and pretreated at thesame time, in particular in a machine, which is provided for thispurpose. In a further process step, all chips are then bonded onto thesubstrate, which is to actually be bonded, or onto the chips, which areto actually be bonded, respectively, at the same time.

In the case of such a collective bond, the planarity of the bond plane,which is formed by all bond surfaces of al chips, represents a qualityfeature, which is to essentially be met. In the ideal case, the bondsurfaces of all chips need to coincide with one another.

Temporary Carrier

The following process describes the production of a temporary carrierwith a plurality of chips, the bond surfaces of which coincide with oneanother, in order to perform a collective bonding process.

In a first process step according to the invention, a first carrier, inparticular a carrier substrate, most preferably a carrier wafer, morepreferably a tape, is coated with a protective layer on a dicing frame.In particular in response to the use of a tape, it is conceivable thatthe protective layer has already been applied to the tape. Apart fromthat, the coating of the carrier can occur with the common, knowncoating methods, such as spin-coating, spray-coating, laminating, etc.

In the alternative, it is also conceivable to provide the surface of thechips with a protective layer. This can already occur prior to cuttingout the chips from the wafer.

In a second process step according to the invention, a plurality ofchips are fixed to the first carrier with a very high alignmentaccuracy. The alignment in particular occurs with the help of alignmentmarks and optical systems. The alignment accuracy is thereby better than1 mm, preferably better than 100 μm, more preferably better than 10 μm,most preferably better than 1 μm, most preferably of all better than 100nm.

The fixation occurs via the later bond surface of the chips. The bondsurfaces of the chips should coincide with one another, if possible. Theprotective layer should furthermore be as thin as possible, have aviscosity, which is as small as possible, and have an elasticity, whichis as high as possible to prevent that the chips penetrate into thelayer at different depths and thus destroy the coincidence of their bondsurfaces. The thickness of the protective layer should preferably be assmall as possible, so as to largely rule out an elastic behavior. Thefirst carrier thus acts as infinitely stiff resistance, the protectivelayer acts exclusively as separator between bond surface and firstcarrier.

The e-module of a tape thereby lies between 1 GPa and 1000 GPa,preferably between 1 GPa and 500 GPa, more preferably between 1 GPa and100 GPa, most preferably between 1 GPa and 50 GPa, most preferably ofall between 1 GPa and 20 GPa. The e-module of polyamides lies between 3and 6 GPa, for example.

The e-module of a stiffer carrier thereby lies between 1 GPa and 1000GPa, preferably between 10 GPa and 1000 GPa, more preferably between 25GPa and 1000 GPa, most preferably between 50 GPa and 1000 GPa, mostpreferably of all between 100 GPa and 1000 GPa. The e-module of somesteel grades lies around 200 GPa, for example.

In a third process step according to the invention, a second carrier, inparticular a carrier substrate, most preferably a carrier wafer, iscoated with an adhesive. The second carrier is the temporary carrier. Incontrast to the protective layer from the second process step accordingto the invention, the adhesive should be elastic and/or plasticallyadaptable, in order to compensate for possible height differences of thechips in such a way that the coincidence of the bond surfaces of thechips is not lost. The adhesive should thus have a viscosity, which isas small as possible, and an option for the lasting deformation.

At room temperature, the viscosity of the adhesive lies between 10E6mPa*s and 1 mPa*s, preferably between 10E5 mPa*s and 1 mPa*s, morepreferably between 10E4 mPa*s and 1 mPa*s, most preferably of allbetween 10E3 mPa*s and 1 mPa*s.

In a fourth process step according to the invention, the rear surfacesof the chips, which are located opposite to the bond surfaces of thechips, are connected to the temporary carrier. The coincidence of thebond surfaces of the chips on the first carrier side is maintainedthereby, while the rear surfaces of the adhesive on the temporarycarrier, if necessary, deform accordingly, in particular due to thepreferably low viscosity. After the bonding process, the thickness ofthe adhesive between a chip and the temporary carrier can thus bedifferent from chip to chip. In an expansion according to the invention,the removal of the adhesive between the chips is possible. An alignmentbetween the first carrier and the temporary carrier preferably occursvia alignment marks, which are located on the first carrier and thetemporary carrier. It is also conceivable that the alignment marks arelocated on the surfaces of the chips and that they are aligned toalignment marks on the temperature carrier. Aligners for aligningsubstrates are described in detail in publications U.S. Pat. No.6,214,692B1, WO2015082020A1, WO2014202106A1.

In a fifth process step according to the invention, the first carriercomprising the protective layer is removed. The adhesive effect betweenthe adhesive, the temporary carrier and the chip is thus in particularhigher than the adhesion between the protective layer and the bondsurface of the chips. In a particularly preferred embodiment accordingto the invention, the protective layer is designed in such a way thatthe detachment from the bond surface of the chip occurs withoutcontamination, in particular completely. If the first carrier is a tape,the latter can be pulled off, which facilitates the removal. It may alsobe necessary to chemically change the protective layer with the help ofchemicals and/or electromagnetic radiation, in particular UV light,visible light or infrared light and/or heat or with regard to themechanical properties, so that it loses or at least reduces its adhesiveproperty.

The bond strength between the protective layer and the chips is therebysmaller than 1 J/m², preferably smaller than 0.1 J/m², more preferablysmaller than 0.01 J/m², most preferably smaller than 0.001 J/m², mostpreferably of all smaller than 0.0001 J/m².

In a sixth, optional process step, the in particular simultaneouscleaning and/or plasma activation of the exposed bond surfaces of thechips occurs. This measure is in particular significant, when theremoval of the first carrier from the bond surfaces of the chips has notoccurred in a completely contamination-free manner. The cleaning of allchips can in particular occur simultaneously this time, which increasesthe throughput of the method according to the invention.

In a seventh process step according to the invention, the simultaneousbonding process of all chips, which are fixed to the temporary carrier,then occurs on a product substrate, in particular a wafer. This alsoincludes the option of bonding the chips on the temporary carrier ontochips, which are already located on the product substrate. This createsan option for successively constructing a chip stack on a productsubstrate. An alignment between the temporary carrier and the productsubstrate preferably occurs via alignment marks, which are located onthe carrier and the product substrate. It is also conceivable thatalignment marks are located on the bond surfaces of the chips and thatthey are aligned to alignments marks on the product substrate.

In an eighth process step according to the invention, the removal of thetemporary carrier from the chip occurs. It may be necessary to changethe adhesive with the help of chemicals and/or electromagneticradiation, in particular UV light, visible light or infrared light,and/or heat, or with regard to the mechanical properties, in particularthe viscosity, so that it loses its adhesive property. The temporarycarrier is preferably a carrier, which is transparent for the photonsfrom a specific wavelength range of the EM spectrum. It is preferably aglass carrier. According to the invention, adhesives can thus be used,which can be destroyed from the rear side with the help of a laser, sothat a debonding option of the temporary carrier from the rear sidethereof is possible.

In a ninth process step according to the invention, the adhesive iscleaned off the rear surface of the chip by means of one of thementioned cleaning methods. After this process step, any further chipscan be stacked on the available chips, so as to construct a chip stackon the product substrate in this way.

The positioning accuracy of the chips on the first carrier according tothe process step two as well as the positioning of the chips on thetemporary carrier by means of the collective bonding process accordingto process step seven is preferably made possible or is at leastsupported, respectively, by means of a self alignment of the chips. Thepositioning accuracy is thereby better than 1 mm, preferably better than100 μm, more preferably better than 10 μm, most preferably better than 1μm, most preferably of all better than 100 nm. The support by selfalignment can only occur when a lateral shifting of the chips relativeto the first carrier and/or relative to the temporary carrier is madepossible. For this purpose, the protective layer on the first carrierand/or the adhesive on the temporary carrier need to havecorrespondingly small shear moduli or need to even provide for a plasticdeformation, so that the chips can shift laterally.

Fixing Support

Instead of using the aforementioned temporary carriers, it isconceivable to fix the chips on a fixing carrier, which hascorresponding fixing elements. The fixing elements can be

vacuum fixations

electrostatic fixations

magnetic fixations

gel pack fixations.

The chips can be fixed directly to the fixing carrier with their rearsurfaces. It is disadvantageous that, in contrast to the mentionedtemporary carrier, no adhesive exists, with the help of which astandardization of the bond surfaces of all chips can take place in oneplane. At best the resilience of a gel pack of the mentioned gel packfixation provides for a similar effect. The ejector devices, which willbe described later, can in particular also be used as fixing carriers.

Ejector Devices

In the further course of the present disclosure, a plurality of devicesand methods will be described, in the case of which the accommodationand fixation of chips is necessary. All disclosed methods and devicesthus refer to the already separated chips and the handling thereof,which, according to the invention, should always occur in such a waythat the bond surface is no longer contaminated, if possible. Theseembodiments, which are identified as ejector device, primarily have thetask of fixing a plurality of chips, which have already been separatedto perform a cleaning process on them and to prepare the bond surfacethereof for the actual bonding process.

Ejector Devices Comprising Depression Design

To treat a first ejector device according to the invention around thebond surface of a chip and to delivery it directly to a bonding process,is the storage of the chips in a carrier. The carrier has depressions,in which chips can be positioned and/or fixed.

In a preferred embodiment, the contours of the depressions are congruentto the contours of the chips. In a further alternative according to theinvention, the contours of the depressions can also differ from thecontours of the chips. The depressions are in particular larger than thechips. The access of a cleaning liquid and/or of a plasma to the sidesof the chips is promoted thereby. The distance between the contours ofthe chip and the contour of the depression is thereby smaller than 5 mm,preferably smaller than 1 mm, more preferably smaller than 0.5 mm, mostpreferably smaller than 0.1 mm, most preferably of all smaller than 0.05mm.

Passages (hereinafter also referred to as lead-throughs), in particularholes, through which a lifting device can lift the chips, so as to makethem accessible for a gripper (hereinafter also referred to as grippinghead), are located on the bottom surfaces of the depressions. In aparticularly preferred embodiment according to the invention, the heightof a chip corresponds exactly to the depth of the depression. The bondsurface to be cleaned and the carrier surface thus coincide. Inparticular a mechanical cleaning process is promoted by means of such anembodiment. Due to the fact that the chips do not protrude from thedepression, they cannot be damaged mechanically. They furthermore do notdisappear in the depression and can thus be reached optimally by alltypes of cleaning devices. The embodiment according to the invention isfurthermore optimally suitable for the plasma cleaning of the chips,because, due to the created seamless flatness between the bond surfaceand the carrier surface, the homogeneity of the used plasma is veryhigh. A high reproducibility and in particular an even cleaning, inparticular an even plasma activation of the bond surfaces are ensureddue to the high homogeneity.

All of the carriers provided in the present disclosure, which are usedin a plasma chamber, should have specific properties. In particular, thecarriers need to be comprised of a conductive material. The carriersthus preferably comprise

electrics, in particular

-   -   a metal, in particular    -   an alloy, in particular        -   steel        -   aluminum        -   stainless steel alloys        -   titanium    -   a conductive ceramic, in particular        -   doped SiC        -   doped Si₃N₄

Metallic carriers are preferably coated to prevent a contamination ofthe chips by the metals. Preferably, dielectrics, in particular oxides,nitrides or carbides are possible as coatings.

The carrier is preferably also embodied in two pieces, so that the chipssit on a metallic disk and a screen, which is comprised of a dielectric,in particular Si, SiC or Si₃N₄, is then attached for the plasmaactivation. In this case, the screen has similar or identical dielectricproperties as the chips. A plasma, which is as even as possible, canthus be ensured. The screen in particular even comprises the samedielectric material as the chips.

The absolute amount of the difference of chip height h and the depth tof the depression is smaller than 1 mm, preferably smaller than 0.5 mm,more preferably smaller than 0.1 mm, most preferably smaller than 0.05mm, most preferably of all smaller than 0.01 mm.

The bond surfaces of a plurality of chips can be treated simultaneouslyby means of the embodiment according to the invention, which results inan extreme efficiency increase of the cleaning of chips, which havealready been separated.

After the ejection of the chip in a well-defined height, a gripping headis used to accommodate and to transport the chip. The gripping headthereby does not fix the chip on the bond surface, which has just beencleaned, but on the fixing surface located opposite to the bond surface.The fixing surface can in particular be contaminated in these processsteps. In further process steps, however, the fixing surface can becomea new bond surface, onto which a further chip can be placed, and thenneeds to be cleaned accordingly.

In the case of the described ejector device, the depth t of thedepression is specified. If chips comprising slightly different chipheights h are fixed according to the invention, their bond surfaces,which are to be cleaned, no longer coincide to one another. It isconceivable in this case that that lifting device performs a heightcorrection of some chips, in particular of the chips, the chip heights hof which are smaller than the depths t of the depressions.

Ejector Device Comprising Attachment Design

A further second ejector device according to the invention is comprisedof a carrier, in which passages, in particular holes, are located. Incontrast to the previous first ejector design, this ejector device doesnot have any depressions. The chips, which are to be cleaned, are fixeddirectly to the carrier surface. The surrounding atmosphere is inparticular separated from the passages with the help of seals. It isthus possible to perform the cleaning of the chips, without performing acontamination of the passages by the cleaning agents, for examplechemicals, such as fluids or ions, from the plasma. Fixing elements,which fix the chips, can be located inside the sealed space.

The fixing elements are at least one of the following fixations

vacuum fixations (preferred)

electrostatic fixations

magnetic fixations

adhesive fixation,

mechanical fixations (least preferred)

Most preferably, vacuum fixations are used, which can evacuate thepassage as well as the space between the seals and which thus ensure apressing of the chip onto the seals. The seals can either be solids, inparticular polymers, or, in particular highly-viscous and/or curedpolymers. The seals are then preferably waxes, adhesives, glues, etc.These polymers need to be replaced routinely, because they are removedover time, in particular by means of cleaning processes, which areperformed.

Masks

In an expansion according to the invention, in particular for thementioned ejector devices, a mask comprising an aperture is used, inorder to protect the bond surfaces of chips from contamination. Thechips are always seized via machine components, which necessarily needto move across the chips. In addition to the actual gripping head and acorresponding arm, on the end of which the gripping head is located,cables and lines also need to be moved. All of these machine elementsnecessarily contribute to the contamination of the bond surfaces of thechips, when they move across them.

In a particularly preferred embodiment according to the invention, arelative movement occurs between the mask comprising aperture and thechips. Preferably, the device, on which the chips are located, moves. Itis also conceivable that the mask moves. For removing a chip, theaperture is positioned above the chip, which is to be removed. Thelifting device lifts the chip, which is to be bonded, beyond the mask.On the upper side of the mask, a gripping head removes the chip via itsrear surface, without touching its bond surface, and transports it to aposition, at which it is further processed. In particular, a capturingof the alignment marks of the chip by means of a first lens occurs asnext step. The chip is then moved under the position, which is to bebonded, and is then positioned and bonded in a highly accurate manner,in particular with the help of a second lens, relative to the position,which is to be bonded. According to the invention, it is thus possiblethat the position, at which the chip is bonded, is located far outsidethe chip removal. The chip can furthermore pass through a plurality ofstations until the actual bonding process, in particular alignmentand/or measuring and/or cleaning, and/or test station, etc. According tothe invention, only the rear surface of the chip is touched during theentire chip transport, but never the bond surface thereof. The grippinghead thus fixes the chip, preferably starting at the time of removalfrom the lifting device until the finalization of the bonding.

In a specific embodiment, the product substrate, on which a chip is tobe bonded, is located directly above the chips, which are to be bonded.All other chips, and thus the bond surfaces thereof, are protected fromcontamination by the mask surface again. The ejector unloads the chipfrom the ejector device and bonds it directly onto a product substrateor onto a chip/chip stack of a product substrate, respectively. The bondsurfaces of the product substrate or of the chips of the productsubstrate, respectively, thereby face the ejector directly, thus pointin the gravitational direction. A contamination of the bond surface ofthe chips, which need to still be ejected, on the ejector device isprevented by the mask. This embodiment according to the invention isless preferred than the above-mentioned embodiment, in the case of whicha gripping head transports the chip to another location and bonds itthere, because no further process steps can be performed at the chip inthis alternative.

For all embodiments, the mask itself needs to be contamination-freethereby. In particular, the mask can be cleaned by means of one of thementioned cleaning methods between an assembly process. The mask ismainly used for bonding processes, in which a substrate, which is to beequipped with chips, is positioned with its bond surface ingravitational direction. The mask according to the invention therebyprevents the transfer of contaminations of the substrate or of movingmachine elements to the chips, which are located below the substrate.The masks are in particular used with the ejector devices, which aredescribed in detail in the present disclosure. In these embodiments, inparticular a rotation and thus a contacting of the chips on their bondsurfaces can be forgone. The exact embodiments are described in detailin other sections of the present disclosure, as well as in a figure andthe corresponding figure description.

A top-down flow furthermore prevails in clean rooms. The air thus alwayscirculates from higher positions into lower positions and thereby dragsalong dust particles. The flow direction also has a disadvantageouseffect on the contamination of the bond surfaces. It is conceivableaccording to the invention that provision is made in the vicinity of thedevices, in which a plurality of chips is fixed to the exposed bondsurfaces, in particular in the mentioned ejector devices or fixingcarriers to machines, which produce a lateral flow to laterallydischarge dust particles.

Bond Head

In a further embodiment according to the invention, a fixing device forfixing and bonding a chip is described. This fixing device is alsoidentified as bond head and describes a machine component, which isresponsible for the fixation, the transport and the bonding of theindividual chips on a bond surface. To be able to utilize the advantagesaccording to the invention of a clean bond surface on the chip, it isnecessary to be able to control the bonding process as much as possible.It is in particular absolutely necessary that a chip does not first bondon the edge, but that a bond wave spreads out from the center of thechip to the outside. The concept of the bond wave is already known tothe person of skill in the art from the wafer-to-wafer (W2 W) bonding.Reference is made here to the publications WO2014191033A1,PCT/EP2016053268, PCT/EP2016056249 and PCT/EP2016069307, only to mentiona few.

In contrast to the mentioned W2 W methods, C2 W methods, however, haveextremely high throughputs. The fixing device moves at a very high speedfrom the pick-up location of the chip to the bond position and back. Dueto the high speeds, which need to be reached quickly, the accelerationsare also relatively high. In particular, the acceleration in the zdirection, i.e. normally to the bond surface, is also very high. Thiswanted physical fact can be used to construct a completely new type offixing device, with the help of which it is possible to convexly form achip simply due to the mass inertia, so as to thus ensure that thecenter of the bond surface of the chip contacts the second bond surfacefirst.

The idea according to the invention is that the fixing device has springelements on the periphery, the spring constant of which is smaller thanthe spring constant of a centrically located spring element. In a veryparticular embodiment according to the invention, the fixing surface isnot supported peripherally at all, i.e. spring elements are forgoneperipherally.

The ratio of the spring constant of a peripheral spring element to thespring constant of a centrically located spring element is therebysmaller than 1, preferably smaller than 0.1, more preferably smallerthan 0.01, most preferably smaller than 0.0001, most preferably of allsmaller than 0.00001.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages, features and details of the invention follow fromthe description below of preferred exemplary embodiments as well as fromthe drawings.

FIG. 1a shows a first process step according to the invention of a firstprocess according to the invention,

FIG. 1b shows a second process step according to the invention of afirst process according to the invention,

FIG. 1c shows a third process step according to the invention of a firstprocess according to the invention,

FIG. 1d shows a fourth process step according to the invention of afirst process according to the invention,

FIG. 1e shows a fifth process step according to the invention of a firstprocess according to the invention,

FIG. 1f shows a sixth process step according to the invention of a firstprocess according to the invention,

FIG. 1g shows a seventh process step according to the invention of afirst process according to the invention,

FIG. 2a shows a first process step according to the invention of asecond process according to the invention,

FIG. 2b shows a second process step according to the invention of asecond process according to the invention,

FIG. 2c shows a third process step according to the invention of asecond process according to the invention,

FIG. 2d shows a fourth process step according to the invention of asecond process according to the invention,

FIG. 2e shows a fifth process step according to the invention of asecond process according to the invention,

FIG. 2f shows a sixth process step according to the invention of asecond process according to the invention,

FIG. 2g shows a seventh process step according to the invention of asecond process according to the invention,

FIG. 2h shows an eighth process step according to the invention of asecond process according to the invention,

FIG. 2i shows a ninth process step according to the invention of asecond process according to the invention,

FIG. 3 shows a first ejector device according to the invention,

FIG. 4 shows a second ejector device according to the invention,

FIG. 5 shows a mask according to the invention with aperture in a firstembodiment according to the invention,

FIG. 6 shows a mask according to the invention with aperture in a secondembodiment according to the invention,

FIG. 7a shows a first process step according to the invention of a selfalignment,

FIG. 7b shows a second process step according to the invention of a selfalignment,

FIG. 8a shows a first process step according to the invention of abonding process with bond head according to the invention,

FIG. 8b shows a second process step according to the invention of abonding process with bond head according to the invention.

Identical components or components with the identical function areidentified with the identical reference numerals in the figures.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1a shows a first process step according to the invention of a firstprocess according to the invention for producing an end product 19according to the first process according to the invention. Allpreparations for the production of a plurality of chips are performed ona substrate 11. The preparations include the production of allfunctional properties of the chip, in particular contacts 13. Grooves 12can furthermore be precut, in order to promote the later separatingprocess. By performing all preparatory steps, a bond surface 7 b canalready be contaminated.

FIG. 1b shows a second process step of the first process according tothe invention, a cleaning step of the bond surface 7 b. The bond surface7 b is in particular cleaned and/or activated by means of plasma and/orwet-chemical methods.

FIG. 1c shows a third process step of the first process according to theinvention, in which a fixation of the substrate 11 onto a carrier, inparticular a tape 15, occurs. A tape surface 15 o is preferably designedin such a way that a fixation of the substrate 11 occurs across the bondsurface 7 b, but that a later removal of the tape 15 does not leave anyresidues on the bond surface 7 b.

FIG. 1d shows a fourth process step of the first process according tothe invention, in which a separation of the substrate 11 into individualchips 7 occurs. According to the invention, the bond surface 7 b of thechips 7 must not be contaminated thereby. In particular in response to amechanical separation by means of a separating device 16, the grooves 12are thus preferably provided in the substrate 11, in order to be able toalready end the separating process above the bond surface 7 b.Separations by means of lasers, in particular by means of the knownstealth technology, by means of chemicals, in particular by means ofetching, preferably by means of dry etching, by means of plasma, etc.are also conceivable.

FIG. 1e shows a fifth process step of the first process according to theinvention, in which the chip 7 is removed from the tape 15 by means of abond head 9, on which fixations 6 are located. The bond head 9 therebyfixes the chip 7 on its rear surface 7 r, so that a contamination doesnot occur on the bond surface 7 b.

FIG. 1f shows a sixth process step of the first process according to theinvention, in which the bond head 9 bonds to the further substrate 11′,after an alignment of the chip 7 has occurred relative to a furthersubstrate 11′. The bond surface 7 b is thereby preferably a hybridsurface, which is comprised of a dielectric surface region 20 and anelectric surface region, represented by the contacts 13. In the case ofsuch a hybrid bond surface, a so-called prebond occurs between thedielectric surface region 20 of the bond surface 7 b of the chip 7 and adielectric surface region 20′ of the substrate 11′.

FIG. 1g shows the end product 19 according to the invention of the firstprocess according to the invention, comprised of the substrate 11′ and aplurality of chips 7. The repetition of the mentioned process steps isconceivable, in order to stack further layers of chips 7 on top of thefirst layer of chips 7.

FIG. 2a shows a first process step according to the invention of asecond process according to the invention, in which a plurality of chips7, which have already been separated, are fixed with the bond surface 7b onto a carrier, in particular a tape 15. The bond surfaces 7 b of thechips 7 had to already be cleaned and/or activated in a precedingprocess. The chips 7 are preferably aligned and positioned by means of abond head 9 of a chip bonder. The enlargement shows the boundary surfacebetween the bond surface 7 b of a chip 7 and the tape surface 15 o ofthe tape 15. A protective layer 17, which preferably also has adhesiveproperties, can be located on the tape surface 15 o. Particularlypreferably, the adhesive property between the protective layer 17 andthe tape surface 15 o, however, is larger than the adhesive propertybetween the protective layer 17 and the bond surface 7 b, so that a bondsurface 7 b, which is as contamination-free as possible, remains inresponse to a removal of the tape 15 in a later process step.

FIG. 2b shows a second process step according to the invention of thesecond process according to the invention, in which a substrate 11″ isprepared as temporary carrier. An adhesive 18 is applied to thesubstrate 11″ by means of a known method, in particular by means of aspin-coating process.

FIG. 2c shows a third process step according to the invention of thesecond process according to the invention, in which rear surfaces 7 r ofthe chips 7 are contacted by means of the bonding adhesive. Thecontacting is in particular preceded by an alignment of all chips 7,which are fixed relative to one another, with regard to the substrate11′. It is also conceivable in this process step that a mechanicalpressure application, which is to ensure the coincidence of the bondsurfaces 7 b of all chips 7 in a plane E, occurs from the tape rear 15r. The plane E is thereby that plane, in which all bond surfaces 7 b ofthe chips 7 are to be located. The plane E should in particular beidentical with the surface of the protective layer 17, which is locatedin the direction of the chips 7. This is in particular relevant, whenthe carrier 15 is a tape. It is conceivable, for example, that a rollerrolls across the tape rear 15 r. However, an application across theentire surface, which results in a homogenous pressure distribution, ispreferable.

FIG. 2d shows a fourth process step according to the invention of thesecond process according to the invention, in which the tape 15 wasremoved from the bond surfaces 7 b of the chips 7. The tape 15 ispreferably pulled off. It can be seen from the enlargement Z1 that theremainder of the protective layer 17 can remain on the bond surfaces 7 bafter the removal of the tape 15. In this, less preferred case, thechips need to be cleaned again in a further process step. After theremoval of the tape 15, the bond surfaces 7 b are preferablycontamination-free. The enlargement Z2 shows an exaggerated illustrationof two chips, which are located next to one another, which differ intheir thicknesses d1 and d2. The resilience of the adhesive 18, however,ensures that the bond surfaces 7 b are located in the same plane E,which represents an important aspect of the process according to theinvention.

FIG. 2e shows an optional, less preferred fifth process step accordingto the invention of the second process according to the invention, inwhich the bond surfaces 7 b of the chips 7 were cleaned by means of acleaning process. The enlargement Z1 does no longer show a protectivelayer 17.

FIG. 2f shows a sixth process step according to the invention of thesecond process according to the invention, in which the temporarycarrier 11″, which is equipped with the chips 7, is aligned relative toa further substrate 11′ and is bonded. According to the invention, thebonding of all chips 7 occurs simultaneously.

FIG. 2g shows a seventh process step according to the invention of thesecond process according to the invention, in which the adhesive 18 istreated. The treatment can occur chemically and/or thermally and/or bymeans of EM waves, in particular by means of UV light or infrared. In aparticularly preferred embodiment according to the invention, thetreatment occurs by means of the temporary carrier 11″. The treatmentpreferably has the result that the adhesive properties of the adhesive18 are reduced or even eliminated completely, so that the temporarycarrier 11″ can be released from the chips 7.

FIG. 2h shows an eighth process step according to the invention of thesecond process according to the invention, in which the carriersubstrate 11″ is removed.

FIG. 2i shows a ninth process step according to the invention of asecond process according to the invention, in which the rear surfaces 7r of the chips 7 are cleaned. Again, the result is an end product 19.

FIG. 3 shows a first embodiment according to the invention for masscleaning and/or plasma activation and/or bonding of chips 7. The chips 7are located in an ejector device 1, which has depressions 2.Lead-throughs 3, in particular simple holes, through which a liftingdevice 4 can lift and lower a chip 7, are attached to the bottom of thedepressions 2. The loading and/or unloading of the chips 7 can occur viaa gripping head 5, which can fix a chip 7 only on its rear surface 7 rwith the help of a fixation 6, in order to transport it. All of the bondsurfaces 7 b of all chips 7 preferably coincide during a mass cleaningand/or plasma activation inside the plane E. The coincidence of all bondsurfaces 7 b has the advantage of the homogenous treatment. It is thusensured in particular in the case of a plasma treatment that the plasmadensity is homogenous across the entire surface. If the chips 7 shoulddiffer slightly in their thicknesses, the lifting devices can perform aslight correction in order to ensure the coincidence of the bondsurfaces 7 b again.

FIG. 4 shows a second embodiment according to the invention for the masscleaning and/or plasma activation and/or bonding of chips 7.

The chips 7 are located in an ejector device 1′, which has seals 8. Thechips 7 can be loaded and/or unloaded by means of a lifting device 4,which can move translationally through lead-throughs 3. The fixationpreferably occurs by means of fixations 6, in particular by means ofvacuum channels, which permit the creation of a vacuum in the space inresponse to a contact of the chip 7 with the seal 8. For the sake ofclarity, the gripping head 5 was not shown in this drawing.

The ejector devices 1, 1′ thus serve for the general mass cleaningand/or plasma activation and/or bonding of separated chips 7. It isfurthermore conceivable that the ejector devices 1, 1′ themselves areconstructed to be so compact that they can be used as carrier wafer 11″in terms of the second process according to the invention. In this case,the bond surfaces 7 b of the chips 7 need to protrude slightly beyondthe ejector surfaces 1 o, 1 o′ at least prior to the bonding process tothe substrate 11, which is automatically fulfilled in structural termsfor the ejector surface 1 o′ of the ejector 1′. In particular theejector device 1′ is thus suitable as a type of fixing carrier. Thefixations 6 can then also be electrostatic, magnetic or gel packfixations.

FIG. 5 shows a first expansion of an embodiment according to theinvention of the bonding, in which the ejector device 1 can be used inan exemplary manner to have a gripping head 5 accommodate a chip 7through an aperture 24 of a mask 23. The accommodated chip 7 istransported, in particular across a plurality of stations. Lenses 25 canthereby measure the bond surfaces 7 b and/or the rear surfaces 7 r ofthe chips 7 and/or the substrate 11′. In particular, a search can beconducted for alignment marks (not shown) on the chips 7 and/or thesubstrate 11′, in order to correctly position the transported chip 7. Inthis expansion, the substrate 11′, which is to be equipped, is thus notlocated directly above the chips.

FIG. 6 shows a second expansion of an embodiment according to theinvention of the bonding, in the case of which the ejector device 1′ canbe used in an exemplary manner, in order to bond a chip 7 through anaperture 24 of a mask 23 to a chip 7 of a substrate 11′. The ideaaccording to the invention lies in that the mask 23, which in particularis comprised of a high-purity material, which preferably does not have asurface contamination, protects the chips 7 on the ejector device 1′,which is used in an exemplary manner, from contamination. According tothe invention, it is thus shown again, how the bond surface 7 b of thechips 7 can be protected from contamination. It goes without saying thatany other type of device can be used instead of the ejector device 1′,which is used in an exemplary manner, in order to guide the chip 7through the aperture 24 and to bond it to the surface, which is locatedon the other side of the mask 23, of another chip 7 or of a substrate11′.

FIG. 7a shows a process step according to the invention of a selfalignment according to the invention of a chip 7 on a substrate 1′. Thechip 7 is placed onto a liquid film 21 by means of a bond head 9. In aparticular embodiment, the liquid film 21 is not distributedcontinuously across the entire substrate 1′, but is present as drop orpuddle only at those locations, at which the self alignment of chips 7is to occur.

A non-optimal alignment of the contacts 13 of the chip 7 with thecontacts 13 of the substrate 1′ can be seen.

FIG. 7b shows a second process step according to the invention of theself alignment according to the invention of the chip 7 on the substrate1′. The bond head 9 releases the fixation to the chip 7. Due to itslateral movability due to the presence of the liquid film 21, said bondhead is now aligned in such a way that the contacts 13 of the chip 7 areas congruent as possible with the contacts 13 of the substrate 1′. Thereason for this lies in the different bonding properties of thedielectric and electric regions. Those regions, which are hydrophilic,preferably attract hydrophilic regions. This interaction can preferablyexpand through media with at least partially polar character. Water is adipole and, according to the invention, is thus particularly wellsuitable for this object.

FIG. 8a shows the bond head 9 according to the invention, including afixing surface 22 comprising fixations 6. Spring elements 10, 10′comprising different spring constants, are located behind the fixingsurface 22. The spring constant of the centrically installed springelement 10 is preferably larger than the spring constants of theperipherally installed spring elements 10′. An acceleration of the bondhead 9 in the lateral direction has no impact on the shape of the fixingsurface 22.

FIG. 8b shows the bond head 9 according to the invention in response toan acceleration in the normal direction of a surface, which is to bebonded. Due to the higher spring constant of the middle spring element10, the inertia acts less strongly on the middle part of the fixingsurface 22 or, in other words, the middle part of the fixing surface 22follows and reacts more quickly than the peripheral part. The curvatureis advantageously also attained by means of the quick approach of thecontact surface and the air cushions, which are present. The dynamicpressure, which is created by means of the translational movement, onthe fixing surface 22 would push the fixing surface symmetrically to theback in the case of identical spring elements. Due to the fact, however,that the peripheral spring elements 10′ have a smaller spring constantthan the middle spring element 10, they yield more easily, because theyare more elastic. In addition to the inertia, the dynamic pressure,which is created, thus also effects a curvature. Due to this mechanicalasymmetry, the fixing surface 22 and thus the chip 7, which is fixedthereto, is thus curved convexly and can create an optimal contact point23 for a direct bond. It is thus ruled out that the chip 7 contactslaterally or flat at first.

LIST OF REFERENCE NUMERALS

-   1, 1′ ejector device-   1 o, 1 o′ ejector surfaces-   2 depression-   3 lead-through-   4 lifting device-   5 gripping head-   6 fixation-   7 chip-   7 b bond surface-   7 r rear surface-   8 seal-   9 bond head-   10, 10′ spring elements-   11, 11′, 11″ substrate-   12 grooves-   13 contacts-   14 frame-   15 tape-   15 o tape surface-   15 r tape rear-   16 separating device-   17 protective layer-   18 adhesive-   19 end product-   20 dielectric surface-   21 liquid-   22 fixing surface-   23 mask-   24 aperture-   25 lens-   d1, d2 thickness-   E coincidence plane-   t depth-   Z1, Z2 enlargements

What is claimed is:
 1. A device for bonding a plurality of chips onto asemiconductor substrate or further chips, wherein the device comprises:an ejector including a storage area for storing the plurality of chips;and a bond head for positioning and aligning a chip of the plurality ofchips, the bond head comprising a first spring element having a firstspring constant, and a second spring element having a second springconstant, wherein the first spring constant is different from the secondspring constant.
 2. The device according to claim 1, wherein the secondspring element comprises at least two spring elements spaced apart fromone another, and the first spring element is arranged between the atleast two second spring elements.
 3. The device according to claim 2,wherein one of the at least two spring elements is arranged on a firstperipheral edge of the bond head and another of the at least two springelements is arranged on a second peripheral edge of the bond head, thesecond peripheral edge positionally opposite the first peripheral edge.4. The device according to claim 3, wherein the first spring element iscentered on the bond head.
 5. The device according to claim 2, whereinthe first spring constant is greater than the second spring constant. 6.The device according to claim 1, wherein the bond head includes a fixingsurface operable to selectively fix the fixing surface to the chip, anda second surface opposite the fixing surface, wherein the second surfaceis arranged between the fixing surface and the first and second springelements.
 7. The device according to claim 1, wherein the first springelement is centered on the bond head.
 8. The device according to claim1, wherein the first spring constant is greater than the second springconstant.
 9. The device according to claim 1, wherein the bond headincludes a fixing device.
 10. The device according to claim 9, whereinthe fixing device comprises at least one vacuum port.
 11. The deviceaccording to claim 1, wherein the storage area comprises a plurality ofcavities each having a through-hole, and a lifting device movable withinthe through-hole to lift or lower a chip of the plurality of chips fromthe respective cavity.
 12. A device for bonding a plurality of chipsonto a semiconductor substrate or further chips, wherein the devicecomprises: an ejector including a storage area for storing the pluralityof chips; and a bond head for positioning and aligning a chip of theplurality of chips, the bond head comprising a fixing surface forselectively fixing the chip to the bond head, a second surface oppositethe fixing surface, and an elastic support coupled to the secondsurface, wherein during acceleration of the bond head in a directionnormal to the fixing surface the elastic support surface is configuredto flex and cause the fixing surface to be non-planar.
 13. The deviceaccording to claim 12, wherein the non-planar surface comprises a curvedsurface.
 14. The device according to claim 12, wherein the elasticsupport comprises a plurality of spring elements, wherein at least twospring elements of the plurality of spring elements have differentspring constants.
 15. The device according to claim 14, wherein theplurality of spring elements comprise first, second and third springelements spaced apart from one another, the first spring elementarranged between the second and third spring elements.
 16. The deviceaccording to claim 15, wherein the second spring element is arranged ona first peripheral edge of the bond head and the third spring element isarranged on a second peripheral edge of the bond head, the secondperipheral edge positionally opposite the first peripheral edge.
 17. Thedevice according to claim 16, wherein the first spring element iscentered on the bond head.
 18. The device according to claim 17, whereina spring constant of the first spring element is greater than a springconstant of the second and third spring elements.
 19. The deviceaccording to claim 12, wherein the storage area comprises a plurality ofcavities each having a through-hole, and a lifting device movable withinthe through-hole to lift or lower a chip of the plurality of chips fromthe respective cavity.